The phosphorus cycle in forest ecosystems as revealed by analysis of the isotopic composition of oxygen associated to phosphate

The current view on the P cycle in forest ecosystems relies mostly on measurements and correlations of pools, and to a lower extent on measurement of fluxes. Previous works do not provide direct insight into the processes phosphate molecules went through at the ecosystem level. For example, we have no direct insight into the processes P molecules go through at the ecosystem level, and into the relative importance of organic and mineral pools in sustaining P nutrition of trees. The analysis of oxygen isotopes associated to P (18Op) is expected to bring this type of information. Our contribution to this project will consist in studying the relative importance of biological and geochemical processes in controlling the P cycle in temperate beech forest ecosystems along a gradient of decreasing soil P availability.

We will follow the fate of phosphate from litter fall to the uptake of P by forest plants via P release by decomposition of organic matter, and after release from P-containing minerals. We will use a multi-isotope approach (O in water, P and O in phosphate, C in organic matter) at natural abundance or under enriched conditions to address our research question. We will rely on measurements in the established forest ecosystems, on laboratory incubations of the organic layer or the mineral soil and on pot experiments with growing plants. To characterize the five sites, we will use isotopic exchange kinetics to determine P-availability in the samples from the quantitative soil pits. Furthermore we will follow the kinetics of microbial P mobilisation and subsequent uptake by the plant.

For further Information,see:
ETH - Plant Nutrition Group
Universität Tübingen - Geoecology